The change comes as a way to solve the users and developers frustration in regard to installing newer software without having to worry about the impact on other applications or the system, because a snap package contains all of its dependencies, so it can't interfere with other packages.

That's not the only advantage snap packages have over traditional deb packages. Snap packages are easy to build, more secure, since they are isolated from the rest of the system, and support transitional updates. Furthermore, snap packages work for PC, Server, Mobile and IoT devices.

"Snap packages enable developers to bring much newer versions of apps to Ubuntu 16.04 LTS. Newer versions of KDE, GNOME, browser or other desktop environment apps will usually build easily on older LTS releases but the complexities of packaging and providing updates have prevented us from delivering them in the past", writes Olli Ries.

He also mentions that "developers of paid apps have often been the most frustrated with having to manage dependencies and compatibility with various libraries, especially on older releases of Ubuntu. For this reason these applications are going to be migrated from debs to snaps by Autumn 2016".

As for deb packages, Ubuntu 16.04 LTS (and newer versions) will continue to support the .deb format, and deb archives will be available to use and distribute software.

Update: a bit more information is available on the Ubuntu developer desktop page, including answers a few questions you might have:

Does it work in any desktop environment?Unity7 is the desktop environment of Ubuntu 16.04 LTS and this feature is primarily targetted at it. Nevertheless, this doesn't prevent it from working with other desktops and more generally Ubuntu derivatives.How does this fit with Unity8 and the convergent desktop?Unity8 is the codebase that will eventually bring all projects under the same convergent interface, it is the future of Ubuntu and this feature will work there as well in due time. Note that you can test Unity8 as a technology preview in Ubuntu 16.04 LTS.Are snaps replacing click and deb packages?Snaps are the next generation of apps for all Ubuntu devices. After an IoT and smart applicances focused launch, we are now introducing them as a technology preview on the classic desktop. Click packages are still the default in Unity8 environments and Debian packages are still at the core of Unity7.